1. Field of the Invention
The invention relates to a rolling bearing cage that is able to suitably support a high-speed rotating shaft of a machine tool, or the like, and an inner ring, cage and rolling element assembly, an outer ring, cage and rolling element assembly and a rolling bearing that are provided with the rolling bearing cage.
2. Description of the Related Art
Japanese Patent Application Publication No. 2004-316757 (JP-2004-316757) describes a rolling bearing used to support a main shaft of a machine tool. The main shaft of the machine tool is supported by different rolling bearings at a tool side and at a side opposite to the tool side. In order to relieve thermal expansion, or the like, of the main shaft, a cylindrical roller bearing that allows an axial displacement of the main shaft is used at the side opposite to the tool side. The cylindrical roller bearing includes an inner ring, an outer ring, a plurality of cylindrical rollers and a cage. The inner ring has a raceway on its outer periphery. The outer ring has a raceway on its inner periphery. The plurality of cylindrical rollers are arranged between the respective raceways of the inner and outer rings so as to freely roll along the raceways. The cage holds the cylindrical rollers at a predetermined interval in the circumferential direction.
In addition, the cage used in the cylindrical roller bearing described in JP-A-2004-316757 is made of synthetic resin. As shown in FIG. 8, the cage includes an axial pair of annular portions 121 and a plurality of cage bar portions 122. The axial pair of annular portions are formed in an annular shape. The plurality of cage bar portions 122 are arranged in the circumferential direction and are spanned between the axial pair of annular portions 121. A pocket 123 is formed between the pair of annular portions 121 and any adjacent cage bar portions 122 in the circumferential direction. Each pocket 123 accommodates a corresponding one of the cylindrical rollers 113. Both ends of each cage bar portion 122 in the circumferential direction each have a protrusion 130 that protrudes toward the pocket 123 and toward a radially outer side. The protrusions 130 of each cage bar portion 122 are formed in a bifurcate shape. When a cylindrical roller bearing that uses the above cage 114 is assembled, first, in the intermediate stage, the cage 114 is placed on the outer peripheral side of the inner ring 112, and then the cylindrical rollers 113 are respectively accommodated in the pockets 123 of the cage 114. By so doing, an inner ring, cage and rolling element assembly is assembled. In a state of the inner ring, cage and rolling element assembly, the cylindrical rollers 113 in the respective pockets 123 are retained by the protrusions 130 so as not to come off radially outward. Then, an outer ring 111 is fitted to an outer peripheral portion of the inner ring, cage and rolling element assembly to thereby assemble the cylindrical roller bearing.
In JP-A-2004-316757, when the main shaft of the machine tool rotates at high speed, contact force between the cage 114 and cylindrical rollers 113 of the cylindrical roller bearing also increases. Therefore, each cylindrical roller 113 accommodated in the pocket 123 bite into between the protrusions 130 on both sides thereof to thereby increase rotational resistance. Thus, in order to support the high-speed rotation of the main shaft by preventing each cylindrical roller 113 from biting into between the protrusions 130, it is required to enhance the rigidity of each protrusion 130.
On the other hand, when the inner ring, cage and rolling element assembly of the cylindrical roller bearing described in JP-A-2004-316757 is assembled, it is necessary that each cylindrical roller 113 is pushed in from the radially outer side into between any adjacent protrusions 130 formed on both sides of the pocket 123 in the circumferential direction to elastically deform the protrusions 130 so as to expand circumferentially outward. Therefore, if the rigidity of each protrusion 130 is excessively high, there is a problem that it is difficult to assemble the cylindrical rollers 113 and, in addition, local stress easily occurs at a proximal portion (particularly, a boundary portion P between an outer peripheral surface 136 and a side surface of each cage bar portion 122) of each protrusion 130.
In addition, the cage used in the cylindrical roller bearing described in JP-A-2004-316757 is made of synthetic resin. As shown in FIG. 9A, the cage includes an axial pair of annular portions 121 and a plurality of cage bar portions 122. The axial pair of annular portions are formed in an annular shape. The plurality of cage bar portions 122 are arranged in the circumferential direction and are spanned between the axial pair of annular portions 121. A pocket 123 is formed between the pair of annular portions 121 and any adjacent cage bar portions 122 in the circumferential direction. Each pocket 123 accommodates a corresponding one of the cylindrical rollers 113.
When a cylindrical roller bearing that uses the above cage 114 is assembled, first, in the intermediate stage, the cage 114 is placed on the outer peripheral side of the inner ring 112, and then the cylindrical rollers 113 are respectively accommodated in the pockets 123 of the cage 114. By so doing, an inner ring, cage and rolling element assembly is assembled. In a state of the inner ring, cage and rolling element assembly, the cylindrical rollers 113 in the respective pockets 123 are retained by the protrusions 130 arranged on both sides thereof so as not to come off radially outward. Then, the outer ring 111 is fitted to the outer peripheral portion of the inner ring, cage and rolling element assembly to thereby finish the cylindrical roller bearing.
In addition, in JP-A-2004-316757, the side surface of each protrusion 130 at the distal end side has an inclined surface 130a as shown in FIGS. 8, 9A, and 9B to thereby make it easy to introduce the cylindrical rollers 113 into the pockets 123; however, an edge portion 130c is present between the inclined surface 130a and a side surface 130b that is continuous with the inclined surface 130a, so there is a problem that each cylindrical roller 113 strongly contacts the edge portion 130e to cause the protrusion 130 to be easily damaged.
In addition, when the main shaft of the machine tool rotates at high speed, each cylindrical roller 113 accommodated in the pocket 123 tries to bite into between the pair of protrusions 130 on both sides thereof. However, an edge portion 130e is present between a concave side surface 130d of the protrusion, formed at the pocket 123 side, and the side surface 130b that is continuous with the radially outer side of the side surface 130d. Therefore, the cylindrical roller 113 strongly contacts the edge portion 130e to thereby damage the protrusion 130 at the edge portion 130e or to generate excessive heat in the protrusion 130 at the edge portion 130e. This has interfered with high-speed rotation of the cylindrical roller bearing.